This invention relates to a semiconductor magnetoresistance device capable of sensing a change of magnetic flux density and useful for detecting rotation, displacement or the presence of magnetic material.
Semiconductor magnetoresistance (MR) devices include magneto-sensitive layers which are preferably made of semiconductors having a high electron mobility such as indium antimonide (InSb) and indium arsenide (InAs). Indium antimonide is most often used because of the highest electron mobility. The InSb magneto-sensitive layers are generally prepared by either a thin film technique such as evaporation or sputtering or a bulk technique such as slicing of a single crystal ingot or polishing of a single crystal piece.
For semiconductor MR devices, a few structures are employed to increase a resistance change represented by RB/R0 wherein RB is a resistance value under an applied magnetic field and R0 is a resistance value in the absence of a magnetic field. A first structure having short-circuiting electrodes formed on a magneto-sensitive layer is disclosed in JP-A 10-70323, JP-A 10-209520, JP-A 10-209523, and JP-A 10-209524. A second structure having high conductivity acicular crystals buried within InSb is disclosed in JP-A 56-60078. In the first structure, as shown in FIG. 4, a semiconductor MR film 102 is formed on a surface of a substrate 101. Short-circuiting electrodes 103 and electrical signal output electrode pads 104 are formed on the semiconductor MR film 102.
Means for altering the resistance value in the absence of a magnetic field of a MR device is generally divided into two: a method of changing the geometrical pattern of the magneto-sensitive layer and a method of changing the thickness of the magneto-sensitive layer.
The method of changing the pattern design has the problems of increased time and cost partly because a brand new photomask must be furnished for the step of patterning the magneto-sensitive layer by photoetching.
In contrast, the method of changing the thickness of the magneto-sensitive layer is simple and inexpensive because the thickness can be adjusted by controlling the deposition time involved in the thin film technique or by controlling the polishing time involved in the bulk technique.
However, the thickness changing method is not compatible with the first structure. If the magneto-sensitive layer is made thick in order to reduce the resistance in the absence of a magnetic field, the short-circuiting electrodes fail to exert their effect in the depth of the magneto-sensitive layer, resulting in a drop of RB/R0.
As to the second structure, increasing the thickness of the magneto-sensitive layer invites little drop of RB/R0. However, if an InSb magneto-sensitive layer with acicular crystals buried therein is crystallized, crystal defects develop, failing to produce an InSb magneto-sensitive layer having a high mobility. No satisfactory RB/R0 is available.
An object of the invention is to provide a semiconductor magnetoresistance device which permits a magneto-sensitive layer to be increased in thickness while preserving a high RB/R0 and thus permits the use of the simple, inexpensive method of controlling the thickness of the magneto-sensitive layer for changing the resistance value in the absence of a magnetic field.
Another object is to provide a method for preparing the semiconductor magnetoresistance device. A further object is to provide a magnetic sensor.
In a first aspect, the invention provides a semiconductor magnetoresistance device comprising a semiconductor magneto-sensitive layer having a pair of opposed surfaces and plural pairs of opposed short-circuiting electrodes formed on the opposed surfaces of the layer.
Preferably, the semiconductor magneto-sensitive layer is formed of indium antimonide or indium arsenide and is a single crystal. In one preferred embodiment, each of the opposed surfaces of the semiconductor magneto-sensitive layer is provided with recesses where the short-circuiting electrodes are formed. Typically the semiconductor magneto-sensitive layer has a thickness of 10 to 50 xcexcm.
The device may further include a substrate on which the semiconductor magneto-sensitive layer is disposed and a protective film disposed between the semiconductor magneto-sensitive layer and the substrate. The substrate is preferably comprised of ferrite and especially Nixe2x80x94Zn base ferrite.
In a second aspect, the invention provides a method for preparing a semiconductor magnetoresistance device as defined above. A photosensitive resin is applied onto one surface of a semiconductor magneto-sensitive layer, and the photosensitive resin is patterned into a negative pattern of short-circuiting electrodes. A metal thin film is formed on the layer surface, and the layer is dipped in a solution in which the photosensitive resin is readily dissolved, thereby removing the portions of the metal thin film that are located on the patterned photosensitive resin, the remaining portions of the metal thin film forming short-circuiting electrodes. A protective film is formed on the short-circuiting electrode-bearing surface of the layer, and the layer at the protective film side is bonded to a substrate. Thereafter, short-circuiting electrodes are similarly formed on the other surface of the semiconductor magneto-sensitive layer. The method may further involve, between the patterning step and the metal thin film forming step, the step of etching the layer through openings in the negative pattern to form recesses in the layer where the short-circuiting electrodes are to be formed.
Also contemplated herein is a magnetic sensor comprising the semiconductor magnetoresistance device defined herein.
When the magneto-sensitive layer is relatively thin, the mere provision of short-circuiting electrodes on both the surfaces of the magneto-sensitive layer increases the likelihood of short-circuiting. Even when the magneto-sensitive layer is relatively thick, the provision of short-circuiting electrodes embedded in both the surfaces of the magneto-sensitive layer enables the short-circuiting electrodes to exert their effect to the deep section or intermediate section of the magneto-sensitive layer. In either case, a high RB/R0 is maintained.